Electrical Agents

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Electrical Agents

  1. 1. Electrical Agents Covering the principles of electricity for electrotherapy found in Chapter 9 of Knight & Draper’s Therapeutic Modalities: the Art and Science (2008) KIN 195
  2. 2. A Common Language <ul><li>To minimize confusion and increase transfer of knowledge, the APTA in 1990 published a common language for electrotherapy. </li></ul><ul><li>Mastering terminology improves electrotherapy education and facilitates discussions of electrical modalities with peers, sales reps, other health professionals, etc. </li></ul>
  3. 3. The Basics of Electricity <ul><li>Static & Current Electricity </li></ul><ul><ul><li>Static electricity is frictional electricity; difficult to discharge other than all-or-nothing </li></ul></ul><ul><ul><li>Current electricity is a stream of electrons passed along a conductor. Current can be passed in a Direct Current (DC), unidirectional flow b/w anode & cathode of a battery. Current can also be passed as an Alternating Current (AC) that rhythmically flows b/w anode & cathode. </li></ul></ul><ul><ul><li>The most common form of electrotherapy is pulsed or interrupted AC. </li></ul></ul>
  4. 4. The Basics of Electricity, cont. <ul><li>Brief Review of Chemistry & Physics </li></ul><ul><ul><li>Know these terms: matter, element, atom, molecule, proton, neutron, electron, electrical charge, ion </li></ul></ul><ul><ul><li>electrolyte (substance w/ ions that is conductive) </li></ul></ul><ul><ul><li>Current Flow: flows from low concentration to high concentration (cathode to anode) </li></ul></ul><ul><ul><li>Conductors transports flow; insulators resists flow; semiconductors can transport with added heat/light/or voltage; partial conductors allow some flow of current under certain conditions </li></ul></ul>
  5. 5. The Basics of Electricity, cont. <ul><li>A Review of Basic Chem & Physics, cont. </li></ul><ul><ul><li>Quantifying Electricity </li></ul></ul><ul><ul><ul><li>Coulomb: unit of charge </li></ul></ul></ul><ul><ul><ul><li>Voltage: force created by concentration gradient of electrons </li></ul></ul></ul><ul><ul><ul><li>Volt: unit of force that pushes current of 1 amp through a resistance of 1 ohm. Commercial voltage is 110 or 220V. </li></ul></ul></ul><ul><ul><ul><li>Ampere: unit of current flow equal to 1C/sec. Lights and motors use hundreds, e-stim use only mA </li></ul></ul></ul><ul><ul><ul><li>Ohm: unit of resistance equal to 1V/A. </li></ul></ul></ul><ul><ul><ul><li>Resistance or Impedance: electricity always flows in path of least resistance. </li></ul></ul></ul>
  6. 6. The Basics of Electricity, cont. <ul><li>Current Flow and Ohm’s Law </li></ul><ul><ul><li>current= force/ resistance or </li></ul></ul><ul><ul><li>Amp (A) = volt (V)/ ohm ( Ω ) </li></ul></ul><ul><ul><li>Example: with 6V and 6000 Ω , what is the A? </li></ul></ul><ul><ul><li>Answer: 0.001 A or 1mA. </li></ul></ul><ul><ul><li>Ex 2: with 100V applied to 20,000 Ω in a muscle, how much current would flow into the muscle? </li></ul></ul><ul><ul><li>Answer2: 5mA </li></ul></ul><ul><ul><li>What are the two ways of increasing current in a circuit? </li></ul></ul>
  7. 7. Electrical Equipment <ul><li>The Generator: either a gas-type generator or a medical device that converts AC or DC into AC, DC, or pulsed </li></ul><ul><ul><li>Recall that terminals must be paired (positive and negative) and closed to complete a circuit. </li></ul></ul><ul><li>Medical Devices are divided into 2 classes </li></ul><ul><ul><li>Neuromuscular electrical stimulators (NMES) cause muscle contraction </li></ul></ul><ul><ul><li>Transcutaneous electrical nerve stimulators (TENS) cause sensory nerve depolarization; some muscle contraction can occur </li></ul></ul><ul><li>Safety Devices include circuit breakers and ground-fault interrupter (GFI); the GFI can trip at 5mA change in as little as 0.025 sec (electrocution can occur from 200mA thru the heart for 1-3 sec) </li></ul>
  8. 8. The Generation of Electricity <ul><li>Chemical Generation of electricity occurs in batteries by the migration of electrons through electrolyte medium from one terminal to another </li></ul><ul><li>Mechanical Power Generation : when electricity is passed through a wire, a magnetic field is created (electromagnetic induction). When insulated wire is moved relative to a magnet, electricity flows in wire. Electrical generators and electrical motors are conceptually based in E-M induction (how are they different?). </li></ul>
  9. 9. Generation of Electricity, cont. <ul><li>Alternating Current Terminology </li></ul><ul><ul><li>Impulse: AC flow in a single direction </li></ul></ul><ul><ul><li>Cycle: 2 impulses </li></ul></ul><ul><ul><li>Frequency: rate measured in cycles/sec (cps) low freq is <1000cps and high freq is >10,000cps </li></ul></ul>
  10. 10. Output Current Characteristics <ul><li>Current Modulation </li></ul><ul><ul><li>Current can be in the form of DC, AC or pulsed. A pulse consists of phases (mono-,bi-,tri- or polyphasic). </li></ul></ul><ul><ul><li>Phase charge (measured in Coulombs) is the total charge in a single phase, the result of amplitude and duration. </li></ul></ul><ul><ul><li>Amplitude (intensity, output) is measured by voltage delivered to electrodes or current through the circuit (including the patient) </li></ul></ul><ul><ul><li>Wave form can be many shapes, but most commonly DC is rectangular & AC is sinusoidal </li></ul></ul>
  11. 11. Commonly Used Wave Forms (Knight & Draper, p. 142) <ul><li>Direct wave form: DC, rectangular (ionto) </li></ul><ul><li>Interrupted DC: rectangular (monophasic) </li></ul><ul><li>Sinusoidal: pure AC (biphasic, IF, Russian) </li></ul><ul><li>Faradic wave: asymmetrical AC w/ spike </li></ul><ul><li>Rectangular: interrupted DC, modulated AC </li></ul><ul><li>Biphasic: symmetrical, balanced, rectangular, pulsed </li></ul><ul><li>Twin pulse wave form: monophasic, pulsed, twin spiked (high volt muscle stim) </li></ul><ul><li>Interferential (IF): symmetrical, sinusoidal, hi freq 2000-5000 Hz AC, using two channels simultaneously </li></ul><ul><li>Russian: 2500Hz AC, polyphasic, symmetrical, sinusoidal, burst modulated every 10msec (50x/min) </li></ul>
  12. 12. Tissue Responses to E- Stim <ul><li>Chemical Effects </li></ul><ul><ul><li>Drives ions of medication into the body; anions to cathodes and cations to anodes </li></ul></ul><ul><ul><li>Iontophoresis uses mild uninterrupted DC to drive medication through skin into tissues </li></ul></ul><ul><li>Magnetic Effects </li></ul><ul><ul><li>Electrical current flows in a conductor, causing a magnetic field to form. Responses of tissues to magnetic fields are poorly understood </li></ul></ul>
  13. 13. Tissue Responses to E- Stim, cont. <ul><li>Kinetic Effects (include sensation & muscle contraction) </li></ul><ul><ul><li>Electricity can help depolarize cells, causing action potentials (obey all-or-nothing law) </li></ul></ul><ul><ul><li>Real nerves are mixes of A- ά , β , γ , δ (motor & sensory), B (autonomic motor), and C (sensory) fibers; larger nerves conduct faster, more responsive, have lower thresholds, shorter durations of response, & shorter refractory periods </li></ul></ul><ul><ul><li>The more Superficial or larger the nerve, the more excitable. (A sensory > motor, & motor nerves > C sensory/pain fibers) </li></ul></ul><ul><ul><li>Frequency of steady stimulation can increase to tetany </li></ul></ul><ul><ul><li>Motor points are the locations where current elicit the greatest muscle contraction, found through trial and error (unique to each patient) </li></ul></ul>
  14. 14. Tissue Responses to E- Stim, cont. <ul><li>Electrodes (3 most common) </li></ul><ul><ul><li>Metal-sponge electrodes, held in place with straps; require sponge to be wet to conduct current </li></ul></ul><ul><ul><li>carbon or silicon rubber electrodes, held in place with straps; require conductive gel </li></ul></ul><ul><ul><li>Adhesive carbon or silicon rubber electrodes, quicker, easier, less durable, more expensive </li></ul></ul><ul><ul><li>Some companies are making a true single use electrode… </li></ul></ul><ul><li>Functions </li></ul><ul><ul><li>Active electrodes are smaller than dispersive electrodes </li></ul></ul><ul><ul><li>Electrode placement technique includes bipolar (bipasic), unipolar (active/ dispersive)—polarity dependent (each pt. is unique), quadpolar (IF) </li></ul></ul><ul><ul><li>Current travels 4x better along muscle fiber than perpendicular to it. </li></ul></ul>
  15. 15. Therapeutic Uses of E- Stim <ul><li>Five types of tissue responses to electricity; four can be therapeutically useful </li></ul><ul><ul><li>Ion migration, where ions move through tissue in response to continuous DC current (iontophoresis) </li></ul></ul><ul><ul><li>Fused response, moderate-amplitude, high frequency pulsed or AC stimulation that facilitates wound healing (twin pulse), edema reduction (twin pulse), and pain reduction (interferential) </li></ul></ul>
  16. 16. Therapeutic Uses of E- Stim, cont. <ul><li>Five types of tissue responses to electricity; four can be therapeutically useful </li></ul><ul><ul><li>Twitch contraction, followed by relaxation from low freq, moderate amp AC facilitates muscle re-education (biphasic, Russian) and tendinitis treatments (twin pulse, biphasic, & Russian) </li></ul></ul><ul><ul><li>Tetanic contraction from high amp, high freq AC (>20-30pps) helps strength development (biphasic, Russian) and spasm reduction (biphasic, Russian) </li></ul></ul>
  17. 17. Phases of the Inflammatory Process <ul><li>Phase I: Acute Phase ( 2 subphases) </li></ul><ul><ul><li>Early (Acute): inflammatory response lasts 2-4 days (includes vasodilation) </li></ul></ul><ul><ul><li>Late (Sub-Acute): continue inflammatory phase which is usually complete in 2 weeks (includes phagocytosis, margination) </li></ul></ul><ul><ul><li>This does not include chronic inflammation </li></ul></ul><ul><li>Phase 2: Tissue Formation (Proliferation) </li></ul><ul><ul><li>Tissue rebuilding approximately 2-3 weeks (includes regeneration and collagen synthesis) </li></ul></ul><ul><li>Phase 3: Remodeling Phase </li></ul><ul><ul><li>Adapt to original tissue </li></ul></ul><ul><ul><li>Continues for up to 1 year post injury </li></ul></ul>
  18. 18. Inflammatory phases

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